Green discharge!

It's been 6 1/2 years since I've had my son, and, every once in a while, I can still squeeze milk from both breasts. The other day, I noticed something dark on my nipple, so I started squeezing it, and there was a "black" discharge coming from my nipple. I wiped it off and it wasn't black, it was a dark green. Has anyone had this happen before?? Going to see my doctor next week, but wanted to get some input from all you ladies. Thanks!!!